Delamination or laminar flaws were sometimes detected during manufacturing and/or plant operations. A laminar flaw is a subsurface flaw parallel to the rolling direction of the plate. Definition of the laminar flaw is provided only in the ASME Boiler & Pressure Vessel Code Section XI and API 579/ASME FFS-1 Code. In addition, the both Codes provide different combination rules for multiple laminar flaws.Besides, a large number of laminar indications were detected in pressure vessels. The observed indications were caused by hydrogen flaking induced during the manufacturing process. The ASME Code Section XI Committees have recently developed a rule that provides a combination methodology for a large number of quasi-laminar flaws.This paper introduces the definitions and combination rules of laminar flaws defined by the ASME and API 579/ASME FFS-1 Codes, and quasi-laminar flaws newly developed by the ASME Code Case.Keywords: laminar flaw, quasi-laminar flaw, subsurface flaw, combination rule, code
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